The present invention relates to a remaining battery capacity indicating apparatus and a remaining battery capacity indicating method suitable for use in indicating the remaining battery capacity of a charge and discharge battery which serves as a voltage supply for electronic devices.
Battery packs including a battery as a secondary cell such as a lithium-ion battery, a Ni—Cd battery and a nickel-hydrogen battery have been supplied so far. It is customary for this battery pack to include a microcomputer to calculate the remaining capacity of the battery and to communicate with an electronic device powered by the battery, peripheral circuits of the microcomputer, and a battery state detecting circuit required by the microcomputer to calculate the remaining capacity of the battery.
Such battery pack may not be charged and discharged endlessly. Also, the maximum number of charge and discharge cycles in which charge and discharge characteristics within a tolerance can be maintained is determined to a certain extent in response to the kind of the battery and the like.
As a technology capable of counting the maximum number of charge and discharge cycles to set the remaining battery capacity, the assignee of the present application has previously proposed a battery pack capable of counting the number of charge and discharge cycles in response to deteriorations of the battery when the battery is deteriorated by charging and discharging and which can accurately determine the remaining battery capacity in response to the deterioration of the battery, its charge and discharge counting method and a remaining capacity setting method of the battery pack (see Japanese Laid-Open Patent Application No. 2000-260486).
Also, as a technology for calculating the remaining battery capacity, the assignee of the present application has previously proposed a battery and a remaining battery capacity calculation method capable of accurately calculating the remaining battery capacity in response to a change of temperature when a temperature change occurs in the battery (see Japanese Laid-Open Patent Application No. 2000-260488).
FIG. 1 of the accompanying drawings is a diagram showing the relationship between a set end voltage and a battery end voltage according to the related art. In order to use an electronic still camera available as an electronic device having a battery mounted on its main body, as shown in FIG. 1, the battery end voltage in the electronic still camera is held at 3.0 V as shown by reference numeral 41 in FIG. 1 and the end voltage of the electronic still camera main body is held at 2.9V as shown by reference numeral 42. Hence, the battery can be used completely until the battery is dead.
However, when a battery having a discharge characteristic in which the battery end voltage is held at 2.6V, as shown by reference numeral 43 in FIG. 1, becomes commercially available on the market, since the related-art electronic still camera main body sets the end voltage to 2.9V because of the battery end voltage of the existing battery, the electronic still camera main body can use the battery at most up to the battery capacity of 2.9V.
As a result, it is to be assumed that the set end voltage will be ended not by the battery end voltage but by the end voltage of the electronic still camera main body. Thus, since the power supply from the battery is ended although some capacity of the battery still remains, there is a disadvantage that the remaining battery capacity time may not be indicated accurately.
FIG. 2 is a diagram showing characteristic curves obtained when discharge characteristics of existing cells and a next-generation cell were measured.
As shown in FIG. 2, when a cut-off voltage is held at 2.5V, while discharge capacities of existing batteries 51 and 52 fall within a range of from 2000 to 2300 [mAh], the discharge capacity of a battery 53 with a different discharge characteristic is increased as large as 2500 [mAh].
FIGS. 3A and 3B are, respectively, diagrams showing remaining battery capacity time indications obtained when a new alloy-based cell is employed by 2.6V-incompatible sets according to the related art and the present invention.
As shown in FIG. 3A, when the related-art 2.6V incompatible set uses the new alloy-based cell with such different discharge characteristic, an initial remaining battery capacity indication 61 indicates 90 minutes. An indication 62 indicates the state in which the end voltage reaches 3.1V after the set was driven for 60 minutes, and a remaining battery capacity indication 63 obtained just before pre-end indicates 30 minutes. However, as shown by an indication 64, the set side is not operated during the initial indication time corresponding to the battery side and the remaining battery capacity indication function may not be operated correctly. As a result, the indication goes to a pre-end indication 65 immediately.
Also, a related-art cell accumulated value characteristic 72 corresponding to the related-art cell discharge characteristic 71 shown in FIG. 4 may be computed by a microcomputer on the battery side. The related-art cell accumulated value characteristic 72 may be calculated in such a manner that it may reach zero when the related-art cell discharge characteristic 71 is changed from a related-art cell full charge accumulated value D12 to the end voltage of 2.9V.
In this case, as shown by reference numeral 75 in FIG. 4, when the related-art set employs a new cell with a discharge characteristic 73, the cell is forced to end at the voltage of 2.9V and hence the set side is ended although the accumulated value still remains. Consequently, the set side may use the new cell during the same discharge time period as the related-art cell discharge time T11.